Linux Checking connected Ip Address and How many Connection

netstat -ntu | grep ':' | awk '{print $5}' | sed 's/::ffff://' | cut -f1 -d ':' | sort | uniq -c | sort -nr

This command will check what Ip Addresses are connected to the machine and how many connection. This was a code used in dosdeflate an anti ddos program written for linux. Check google for dosdeflate.